The goal of the FIRCA application is to study the molecular mechanisms of glutamate release from astrocytes. In the parent grant, the PI has shown that calcium signals in astrocytes cause the release of glutamate that in turn can modulate synaptic transmission. Additionally, it has been shown that SNARE proteins are necessary on the release of glutamate from these non-neuronal cells. Given the existing knowledge of the role of SNAREs in mediating excitocytosis, this leads to the hypothesis that exocytosis of glutamate filled vesicles underlies glutamate release from astrocytes. In order to test such a hypothesis it is necessary that the PI work with Dr. Robert Zorec (Slovenia) to measure the capacitance of astrocytes, an assay of exocytosis, a goal that is beyond the scope of the parent project. Through this collaboration four specific objectives will be addressed in this FIRCA project. Specific Aim I: Do elevations of intracellular calcium increase the membrane capacitance of astrocytes? Specific Aim II: Are SNARE proteins required for calcium-regulated changes in cell membrane capacitance? Specific Aim III: Do exocytotic events cause glutamate release from astrocytes? Specific Aim IV. We will determine whether we can detect exocytosis of a single vesicle from astrocytes. We expect that the results of this work, will contribute significantly to our understanding of whether glutamate release from astrocytes is mediated by regulated exocytosis. The clarification of the hypothesis that exocytosis is associated with glutamate release is of fundamental importance for the understanding of the role of astrocyte participation in neuronal plasticity.